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Not All Processed Meats May Hold Same Cancer Risk

Researchers from Queen’s University Belfast in Northern Ireland, United Kingdom (UK), have questioned the World Health Organization’s (WHO) blanket classification of processed meat as carcinogenic after finding significant evidence gaps between processed meat treated with nitrites and nitrite-free processed meat.

Brian Green, PhD; William Crowe, PhD; and Chris Elliott, PhD, all from the Institute for Global Food Security (IGFS) at Queen’s, reviewed existing peer-reviewed literature on the relationship between processed meat and the development of bowel, colon, and rectal cancers. The results of their meta-analysis have been published in the journal Nutrients.

The researchers found that not all processed meats carry the same level of cancer risk. They initially reviewed all recent English-language studies into consumption of processed meat and cancer risk and found the results inconclusive—around one-half of the studies evidenced a link with colorectal cancer. This explains the appearance of contradictory claims in the media in recent years.

But when the researchers isolated research that tested only the consumption of processed meat containing sodium nitrite—a preservative used to extend shelf life and enhance color—evidence of a link with colorectal cancer jumped from one-half to just under two-thirds—65%.

“When we looked at nitrite-containing processed meat in isolation—which is the first time this has been done in a comprehensive study—the results were much clearer,” Crowe explains. “Almost two-thirds of studies found a link with cancer.”

The WHO classified all processed meat—including bacon, sausages, and ham as well as continental European products such as prosciutto and salami—as carcinogenic in 2015.

Not all processed meat, however, contains nitrites. British and Irish sausages, for example, aren’t processed with nitrites, even though many of the continental European and US sausage equivalents—such as hot dogs, pepperoni, and chorizo—are. Some newer types of bacon and ham, processed without nitrites, also are appearing on the market.

In its 2015 statement, the WHO didn’t distinguish between processed meats containing nitrites and those without. Based on the results of their meta-study, the IGFS researchers now believe there’s a need to define the health risk of both types of processed meat separately.

Coauthor Elliott, who carried out the UK government’s inquiry into food safety after the horsemeat scandal, says this latest research brought more clarity to what has been a confusing area for the food industry and the public.

He says, “Because there have been conflicting claims in the scientific community and the media about which types of meat may be carcinogenic, this study couldn’t have come at a better time. It brings much-needed rigor and clarity and points the way for further research in this area.”

So should the public immediately stop eating processed meat containing nitrites? “It’s important we eat a healthy, balanced diet in line with the [UK] government’s ‘Eatwell Guide,’” Green says. “The current Department of Health guidance advises the public to consume no more than 70 g of red or processed meat per day.

“That remains the guidance, but we hope that future research investigating the link between diet and colorectal cancer will consider each type of meat individually rather than grouping them together. Our findings clearly show that not all processed meats, for example, carry the same level of risk.

“There is more research to be done before we can definitively prove causality regarding processed meat and cancer; there are so many variables when it comes to people’s diets. But based on our study, which we believe provides the most thorough review of the evidence on nitrites to date, what we can confidently say is that a strong link exists between nitrite-containing processed meat, such as [hot dogs], and colorectal cancer.”

The IGFS team intends following up its evidence review with a preclinical study probing the effects of nitrite-containing meat on colorectal cancer.